RE-123-based oxide superconductors (REBa2Cu3O7-X: RE represents rare earth elements including Y) exhibit superconductivity at the temperature of liquid nitrogen and have low current losses and are thus extremely promising materials in a practical sense. There is demand for these oxide superconductors to be processed into wires and be used as conductors or electromagnetic coils which is used in power supply or the like.
As an example of a structure in which this oxide superconducting wire is used, an oxide superconducting wire obtained by using a substrate made of a metal having a high mechanical strength, forming an intermediate layer having a favorable crystal orientation on the surface of the substrate using an ion-beam-assisted deposition method (IBAD method), forming an oxide superconducting layer on the surface of the intermediate layer using a film-forming method, and forming a metal-stabilizing layer made of a highly conductive material such as Ag on the surface of the oxide superconducting layer is known.
When a magnetic field component varying in a direction perpendicular to the surface over time is applied to an oxide superconducting wire, loop-like shielding currents flow in the surface of an oxide superconducting layer. The shielding currents cause magnetization losses in which the shielding currents are discharged as heat. Therefore, when large shielding currents are generated, there has been a problem in that the energy efficiency of the oxide superconducting wire decreases. In addition, when the oxide superconducting wire is processed into a coil shape and is supplied with currents so as to generate a magnetic field, the magnetic field is shielded due to the shielding currents, and there has been a problem in that a magnetic field cannot be generated as designed.
In addition, the shielding currents attenuate over time. Therefore, in a case in which an oxide superconducting wire is applied to a superconducting device generating a magnetostatic field which does not change over time, there has been a problem in that the magnetic field changes over time due to the attenuation of the shielding currents.
The shielding currents and the degrees of magnetization losses caused by the shielding currents depend on the width of the oxide superconducting layer. Therefore, it is known that, when an oxide superconducting wire is divided into a plurality of wires, and the wires are thinned (formed into multiple filaments), the shielding currents and the magnetization losses can be reduced.
In addition, it is known that, in a case in which an oxide superconducting wire is used in a device to which an alternating-current is applied such as a motor or a transformer, when the oxide superconducting wire is divided into a plurality of wires, and the wires are thinned, it is possible to reduce alternating-current losses caused by a variable magnetic field based on the flowing alternating-current.
As an example of a method of dividing the oxide superconducting wire into a plurality of wires and thinning the wires, a method in which grooves are formed by radiating laser light rays in the longitudinal direction of the wire from the upper surface thereof and an oxide superconducting layer is divided (for example, Patent Documents 1 and 2) or the like is known.